Xerographic developing apparatus



June 28, 1960 H. E. CRUMRINE 2,942,573

XEROGRAPHIC DEVELOPING APPARATUS Filed April 1, 1958 2 Sheets-Sheet 1'mvzzmozz Herbert E.Crumr|ne ATTORNEY June 28, 1960 H. E. CRUMRINEXEROGRAPHIC DEVELOPING APPARATUS 2 Sheets-Sheet 2 Filed April 1, 195aINVENTOR.

KOPUUJJOU FWDO Herbert E.Crumrine ywflwo ATTORNEY United States Patent2,942,573 XEROGRAPHIC DEVELOPING APPARATUS Herbert E. Crumrine,Rochester, N.Y., a'ssiguor to Haloid Xerox Inc., a corporation of NewYork Filed Apr. 1, 1958, Ser. No. 725,702 9 Claims. (Cl. 118'637) Thisinvention relates to the held of xer'o'gra'phy and in particular to animproved device for use in the development of xerographic images. l V

In the art of xerograpny an electrostatic latent image is formed on aninsulating surface, such as, for example, a hotoeonductive insulatinglayer or electrophotographic surface by the combined action of anelectric field applied through a photoconductive material and action oflight or suitable activating radiation on the photoconductive material"to cause selective conductivity in accordance with the pat-tern ofradiation to which the material is exposed. The result of this combinedexposure and field is to form a pattern of electric charge on thephotoco'nductive layer that is known in the art as an electrostaticlatent image which is capable of utilization, for example, by depositionthereon of finely divided material, such deposition being known in theart as development.

It has been found by others in the art of xerography, as disclosed inLandrigan Patent 2,725,304 and Hayford Patents 2,808,023 and 2,817,598that an electrostatic latent image can be developed very satisfactorilyby presentihg to the image surface a cloud of charged powder particleswith a conductive surface or development electrode positioned closelyadjacent to the image surface, preferably at a distance therefrom in theorder of about to A of an inch or in some instances even closer than 0inch. It has also been found by others in the art of Xerography that oneeffective way of preparing a cloud of substantially uniformly chargedparticles is to form a powder cloud in a suitable cloud generator and topass the cloud under conditions of turbulence through a restrictedopening, such as, for example, a capillary tube.

Basic to the use of the development electrode is the desire to reproducecopies of the original image of high quality and Without distortion.Electrostatic lines of force exist between the electrostatic charges onthe photoconductive insulating layer and areas of different chargepotential. When large area carrying electrostatic charges exist, thelines of force which are present due to charges in the central area ofthe large area tend to run inward through the photoconductive insulatinglayer to the conductive backing member which is the nearest surfacecarrying a different potential. Lines of force running fromelectrostatic charges near the external boundaries of this large areawill tend to extend outward and around the outside border of the largearea at which point their paths will extend inward through thephotoconductive insulatim layer .to the conductive backing member..Development of such an electrostatic :latent image creates depositionwhich relates to the paths taken by the electrostatic lines of force ordevelopment of the electrostatic fields. Therefore, development of alarge area as has just been described tends to reproduce copies withhollow centers and emphasized edges. To prevent such development asurface is positioned at a slight distance the photoconductiveinsulating layer during development. surface, the development electrode,is composed of a conductive material and, in the case ofpositive-to-posi- 2,942,573 Patented June 28, 1960 tive reproductions,is usually maintained at about the same potential as the lowest chargeon the photoconductive layer; whereas, in negative-to-positivereproduction, is usually maintained at a potential equal to the highestcharge on the photoconductive layer. In this manner, a surface is formedthat causes an increase in the lines of force extending outwardly fromthe plate member, thereby creating electrostatic fields which whendeveloped produces distortion-free and fringe-free high quality copy.

In Xerographic development according to these methods there are manyinherent problems caused, among other things, by the need for working inan extremely confined space and with extremely fine tolerances, thisneed being brought about by the narrow space between the image surfaceand the development electrode. For example, the usual development of axerographic image involves uniform deposition of powder particles orother finely divided particulate material, across an area of normalpicture size which may, for example, be an area whose smallest dimensionis several inches or an area Whose smallest dimension is a foot or more.The introduction of a cloud uniformly across this entire area in :1development space in the order of eg to inch thick has obviouslypresented many serious problems.

Many of .the devices used heretofore for powder cloud development havebeen characterized by various shortcomings. For example, when the powdercloud in its flow travels over an area that should be white and thenover an area that should be dark, the leading edge of the dark area isnot always properly developed. Frequently on the developed image thedark area appears to be torn so that a white background shows through.Because of this appearance the flaw is referred to as tearing. Anotherdifliculty occurs when the powder cloud travels over a large, dark areaand then over a large area that should remain white. Although the whitearea is void of charge, it does not always remain free of powder. Developer particles may deposit in streaks through this area in amountsroughly proportional to the length of the dark area that immediatelyprecedes the white area. This diificulty is termed streaking. Stillanother difiiculty is that developed images are not always uniformlydeveloped end-.to-end nor does extending the development time remedythis defect as, apparently, part of the charge in the image areas at oneend of the plate are erased in the development process. Anotherdifficulty encountered is that powder particles, striking the surface ofthe Xerographic plate as a result of mechanical forces, will not onlyadhere .to the plate regardless of the charge on the plate, but thepowder particles will also abrade the surface of the plate therebyreducing the life of the Xerographic plate in terms of the number ofquality reproductions that can be made by the plate.

It is therefore an object of this invention to improve xerographicdeveloping apparatus for reproducing copies of the original image ofhigh quality and without distontion.

Another object of the invention is to improve xerographic developingapparatus to attain a uniformly distributed flow of powder particlescarried by an air stream over a moving electrophotographic plate surfacein a man ner free from localized concentrations or powder-starved zonesor streaks, and free from agglomerations of powder particles.

These and other objects of the invention are attained by means of axerographic developing apparatus in the form of .a manifold assemblypositioned in closely spaced relation to the path of movement of aXerographic plate whereby a development zone is formed bet-ween themanifold assembly and the xero-graphic plate, tl e manifold assemblycontaining a pair of oppositely directed entrance slots for flowingdeveloping material into the developmen-t zone, and multiple exhaustslots for withdrawing excess developing material from the developmentzone. For a better understanding of the invention as well as otherobjects and further features thereof, reference is had to the followingdetailed description of the invention to be'read in connection with theaccompanying drawings, wherein:

Fig. l is a perspective view of the developing apparatus, partiallybroken away to illustrate the various elements of the device, and

Fig. 2 is a detail vertical sectional view of the developing apparatustaken along line 2-2 of Fig.1.

JFigures 1 and 2 show the developing apparatus and related parts with axerographic plate in position for development. The xerographic plate 10,which forms no part of the subject invention, consists of aphotoconductive insulating layer coated on a conductive backing, and issupported on carrier block 11 which in turn rests on drive rolls r12 formovement relative to the developing apparatus. The developing apparatusis mounted to maintain a, uniform close spacing between its lowersurface and that of the xerographic plate whereby to form a developmentzone 13.

The developing apparatus, generally made of metal or other conductivematerial, is essentially a manifold or manifold assembly which containstwo entrance slots, through each of which a stream of fine,electrostatically charged development powder particles suspended in airare directed into the development zone in substantially laminar,parallel flow to the xerographic plate, and which also contains threeexhaust slots through which any excess powder particles are removed fromthe development zone.

In theembodiment disclosed, the manifold or manifold assembly, generallydesignated 14, includes a development wall portion or electrode element15 consisting of plate 16 having deflector plates 17 fastened to theundercut portions 18 of the plate '16, for reasons which will beexplained in more detail hereinafter. To prevent warping of the bottomof the plate 16 during machining, the plate is a casting having threevertical risers 19, 20 and 21 and the reinforcement ribs 22 formedintegral therewith, the ribs 22 being perforated at 23 to permitmounting the plate 16 to a structural element (not shown) of axerographic device.

A pair of riser blocks 25 are attached to the top of plate 16, thegaskets 26 being positioned between the plate 16 and the riser blocks25.

The electrode element .15 contains a pair of entrance slots 27, througheach of which a stream of fine, electrostatically charged developmentpowder particles suspended in a fluid, commonly called a powder cloud,is directed into the development zone 13. The walls of each of the slots27 are formed by the beveled surface of the undercut portions 18 of theplate 16, and the tapered portions of the deflector plates 17. Eachentrance slot 27 extends transversely across the electrode element 15,terminating just short of the outer margins of the electrode element sothat the powder cloud is retained in the development zone. Each entranceslot forms an acute angle with the plane of the bottom surface of theplate 16, and each slot is inclined toward the center of the plate.Preferably, this angle'should approach zero, but as a practical matterit is usually on the order of from 2 to 5 because the deflector platesmust be made of suflicient thickness to minimize excessive wear.

' Each of the entrance slots'27 is supplied with 'a powder cloud by aconventional type powder cloud generator 28,- such as those described inHayford Patent 2,812,883 and Andrus et al. Patent 2,815,330. The powdercloud, by whatever means produced, is then charged. Where a cloud of drypowdered developing material is used, any method of generating the cloudwill almost necessarily produce a charge thereon. For some purposes, thecharge so produced will be adequate. If it is desired to produce a moreuniform charge, however, other charging devices 29, such astriboelectric charging (as by passing the electroscopic powder through anarrow tube of suitable material in turbulent flow), corona charging orother charging device, may be used.

Although any convenient means may be employed to deliver developingmaterial to the developing zone, the preferred construction for thispurpose, as disclosed herein, is similar to the system disclosed andclaimed in copending application, Serial No. 725,558, filed April 1,1958, in the names of Richard E. Hayford and Carl B. Kaiser. In thissystem, the charged powder cloud is delivered to each entrance slot 27by means of conduit 30, elbow 31, inlet conduit 32 and expansion chamber33. The inlet conduits 32 and expansion chambers 33 are formed both inthe plate 16 and riser blocks 25.

An exhaust slot 35 is formed in the center of the plate 16, between theentrance slots 27, the exhaust slot 35 as well as the later describedauxiliary exhaust slots 42, extends transversely across the plate 16,terminating just short of the outer margins of the plate 16. The exhaustslot 35 communicates with a bored passage 36 extending transverselyacross the full width of the riser block 20, the passage 36 being closedby end plates 37 secured by fasteners 38. a In Fig. 1, an end plate 37is shown secured to the riser 21, while the end plate has been removed.from the riser 20, and riser 19 and the corresponding portion of theplate 16 has been broken away, to more clearly illustrate theconfiguration of the various elements.

Communicating with the passage 36 is an exhaust outlet passage 39 thatis connected by means of conduit or vacuum line 40 to a convenient formof dust collector 41 which may comprise a suction pump connected to adust filter.

A pair of auxiliary exhaust slots 42, similar to exhaust slot 35, isformed outboard of the entrance slots 27. Each auxiliary exhaust slot 42communicates with an auxiliary passage 43, similar to passage 36, andthese passages 43 are also closed at their outer ends by end plates 37.Communicating with each auxiliary passage 43 is an auxiliary outletpassage 44 that is connected by conduit or vacuum line 45 to dustcollector 41.

The passage 36 and each of the auxiliary passages 43 are each connectedto damper openings 46 which can be closed by damper plates 47 movablysecured to the risers by screw fasteners 48.

In operation, assume that the photoconductive insulati-ng layer of thexerographic plate 10 bears an electrostatic image. The drive rolls 12,actuated by a power means (not shown) will transport the carrier block11 with the xerographic plate 10 relative to the developing apparatus.As the xerographic plate passes the developing apparatus, a powdercloud, supplied by the powder cloud generator 28, is introduced into thedevelopment zone formed by the xerographic plate and the developingapparatus through the entrance slots 27. The powder cloud deliveredthrough the entrance slots 27 is continuous and from oppositedirections. The center exhaust slot 35 connected to a souce of negativepressure, dust collector 41, draws in most of the powder cloud from eachentrance slot, and in so doing causes the powder cloud streams to travelacross the xerographic plate in a substantial laminar flow, and beforethe opposed flows can collide and thereby cause turbulence, thepowdercloud is withdrawn from the development zone.

No powder cloud should near a plate bearing a latent image where thereis no electrode because reversal development is effected by virtue ofthe bias, field between the xerographic plate and .the developmentelectrode. Powder which would therefore develop a charged and exposedplate without an electrode present would be damaging to thesensitometric quality of the resultant dust image. If, therefore, a longxerographic plate is passed over a relatively short electrode element,escaping powder must be disposed of before it can deposit on a mil 5..

charged surface of the xerographic plate. This powder, if not caught,causes peculiar reversed reversal effects, whereby powder is depositedin areas that should be free of powder. Thus, the auxiliary exhaustslots 42 connected to the dust collector 41 are used to trap and removeall excess powder which could deposit on the plate.

With the xerographic plate moving past the developing apparatus andtherefore past each entrance slot which introduces a flow of powdercloud from separate directions, a uniform distributed amount of powdereddeveloping material is applied over the xerographic plate. Since theflow of powdered developing material is substantially parallel to thexerographic plate, only electrical forces attract the powdereddeveloping material to the xerographic plate and not mechanical forces.

The resultant dust images, developed by the subject developingapparatus, are uniformly developed end-toend with no streaks or tears,because the simultaneous introduction of two streams of powdereddeveloping material from opposite directions over the moving xerographicplate eliminates streaking and tearing, the buildup of powder on oneedge of a dark area due to developing material flowing from onedirection being counteracted by a buildup on the other edge of the darkarea by developing material flowing from the opposite direction.

The xerographic plate and the development wall portion or electrodeelement may be in the shape of flat members, as shown, or, if desired,they may be curved to fit on a drum for continuous operation. Althoughnot shown, it is obvious that the development apparatus may bepositioned within a container of suitable design so as to prevent lossof developer powder to external areas or merely to improve theappearance of the apparatus. Since the image-bearing member has alight-sensitive surface, it is desirable that the apparatus bepositioned in a light-tight enclosure prior to development.

While there have been shown and described the fundamental novel featuresof the invention as applied to a preferred embodiment, it will beunderstood that various omissions and substitutions and changes in theform and details of the device and in its operation may be made by thoseskilled in the art, without departing from the spirit of the invention.It is the intention, therefore, to be limited only as indicated by thescope of the following claims.

What is claimed is:

l. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is movedrelative to the developing apparatus during a developing operation, saiddeveloping apparatus including a manifold assembly having an electrodeelement in closely spaced relation to the path of movement of axerographic plate whereby a development zone is formed between theelectrode element and a xerographic plate during a developing operation,three exhaust slots, for Withdrawing excess developing material from thedevelopment zone, in said electrode element extending transverselythereof, each of said exhaust slots being connectable to a vacuum line,and two entrance slotsin said electrode element for flowing developing'material into the developing zone, one of said exhaust slots beinglocated between said entrance slots, the other two of said exhaust slotsbeing positioned, one each, on opposite sides of and outboard of saidentrance slots, each of said entrance slots forming an acute angle withthe plane of said electrode element and each of said entrance slotsbeing inclined toward the center of said electrode element, each of saidentrance slots being connectable to a source of powdered developingmaterial.

2. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is positionedin closely spaced relationship to the developing apparatus, saiddeveloping apparatus including a manifold assembly having anelectrically conductive development wall portion conformable with thesurface of the xerographic plate, at least three exhaust slots in saiddevelopment wall portionextending transversely thereof, each of saidexhaust slots being connectable to a vacuum line, at least twooppositely directed entrance slots, one each of said entrance slotsbeing positioned between each grouping of said exhaust slots in saiddevelopment wall portion, each of said entrance slots forming an acuteangle with the plane of said development wallportion, and each of saidentrance slots being connectable to a source of powdered developingmaterial.

3. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is positionedin closely spaced relationship to the developing apparatus, and whereinthe electrostatic latent image is developed by a powdered developingmaterial delivered through said developing apparatus, said developmentapparatus including a manifold assembly having an electricallyconductive development wall portion conformable with the surface of thexerographic plate, an exhaust conduit means in said manifold, one end ofsaid exhaust conduit means extending transversely of and across thecenter of said development wall portion of said manifold, the other endof said exhaust conduit means being connectable to a vacuum line, and afirst inlet conduit means and a second inlet coduit means in saidmanifold located on opposite sides of said exhaust conduit means, oneend of said first inlet conduit means and one end of said second inletconduit means extending transversely of said development wall portion ofsaid manifold and at opposed angles with the plane of said Wall portionto form oppositely directed inlets for a powdered developing material,the other end of said first inlet conduit means and the other end ofsaid second inlet conduit means being connectable to a source ofpowdered developing material.

4. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is positionedin closely spaced relationship to the developing apparatus for relativemovement therewith, said developing apparatus including a manifoldhaving an electrically conductive development wall portion, a centerexhaust slot in said development wall portion extending transversely ofsaid development Wall portion, conduit means in said manifold connectedat one end to said center exhaust slot and being connectable at itsother end to a vacuum line, a first entrance slot and a second entranceslot in said develop ment wall portion located on opposite sides of andparallel to said center exhaust slot and in oppositely inclined positionwith respect to each other, said first and second entrance slots beingconnectable to a source of powdered developing material, a firstauxiliary exhaust slot and a second auxiliary exhaust slot in saiddevelopment wall portion positioned outboard of said first entrance slotand said second entrance slot, first and second auxiliary conduit meansconnected to said first and second auxiliary exhaust slots forconnecting said first and second exhaust slots to a vacuum line, anddamper means connected to each of said first and second auxiliaryconduit means and to said conduit means for regulating the flow ofadditional air through said last mentioned means.

5. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is positionedin closely spaced relationship to the developing apparatus fordevelopment by a powdered developing material, said developing apparatusincluding a manifold having an electrically conductive development wallportion, an exhaust means in said manifold, said exhaust means includinga narrow exhaust slot extending transversely of and in the center ofsaid development wall portion and an outlet passage connectable to avacuum line, and at least one powder cloud conduit means on each side ofsaid exhaust means, each said powder cloud conduit means including anarrow entrance slot in said development wall portion inclined towardsaid exhaust slot so that flow from said entrance slot is toward saidexhaust slot, and a powder cloud inlet conduit connectable to a sourceof powdered developing material.

6. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is positionedin closely spaced movable relationship to the developing apparatus, andwherein the electrostatic latent image is developed by a powdereddeveloping material delivered through said development apparatus, saiddeveloping apparatus including an electrically conductive manifoldhaving a development wall portion conformable in shape with the surfaceof the xerographic plate, an exhaust conduit means in said manifold, oneend of said exhaustconduit means having a narrow exhaust slot extendingtransversely of and across the center of said development wall portionof said manifold,vthe other end ofsaid exhaust conduit means beingconnectable to a vacuum line, a first inlet conduit means and a, secondinlet conduit means in said manifold located on opposite sides ofsaidexhaust conduit means, one end of said first inlet conduit means having.an inclined first entrance slot and one end of said second inletconduit means having an inclined second entrance slot extendingtransversely of said development Wall portion of said manifold saidsecond entrance slot being inclined in an opposite direction from saidfirst entrance slot, the other end of said first inlet conduit means andthe other end of said second inlet conduit means being connectable to asource of powdered developing material, and a first auxiliary exhaustconduit means and a second auxiliary exhaust conduit means in saidmanifold outboard of said first inlet conduit means and said secondinlet conduit means, respectively, one end of said first auxiliaryexhaust conduit means and one end of said second auxiliary exhaustconduit means each terminating in an auxiliary exhaust slot extendingtransversely of said development wall portion of said manifold, theother end of said first auxiliary exhaust conduit means and the otherend of said second auxiliary exhaust conduit means being connectable toa vacuum line.

7. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is positionedin closely spaced movable relationsihp to the developing apparatus fordevelopment by a powdered developing material, said developing apparatusincluding a manifold having an electrically conductive development wallportion, an exhaust means in said manifold, said exhaust menas includinga narrow exhaust slot extending transversely of said development portionand an outlet passage connectable to a vacuum line, a pair of powdercloud conduit means in said manifold, each said powder cloud conduitmeans including an entrance slot in said development wall portion, saidentrance slots being located on opposite sides of, inclined toward, andparallel to said exhaust slot, and a powder cloud inlet conduitconnectable to a source of powdered developing material, and a pair ofauxiliary exhaust means in said manifold, each of said auxiliary exhaustmeans including an auxiliary exhaust slot extending trans versely ofsaid development wall portion, one each of said auxiliary exhaust slotsbeing located outboard of each of said entrance slots, and each saidauxiliary exhaust means including an auxiliary outlet passageconnectable to a vacuum line. 7

j 8. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is positionedin closely spaced movable relation to the developing apparatus, saiddeveloping ap: paratus including an electrically conductive manifoldhaving a development wall portion conformable to the xerographic plate,a pair of oppositely directed entrance slots in saidwall portionpositioned adjacent opposite ends of said development wall portion, eachof said entrance slots being connectable to a source of powdereddeveloping material, a first exhaust slot in said wall portionpositioned between one of said entrance slots and the respective end ofsaid development wall portion, a second exhaust slot in said wallportion positioned between the other said entrance slot and itsrespective end of the development wall portion, and a third exhaust slotin said wall portion positioned intermediate said entrance slots,

, each of sai drexhaust slots being connectable to a vacuum line.

9. A developing apparatus for use in a xerographic machine wherein axerographic plate carrying an electrostatic latent image is positionedin closely spaced movable relation to the developing apparatus, andwherein the electrostatic latent image is developed by a powdereddeveloping material delivered through said developing apparatus, saiddevelopment apparatus including a manifold assembly having anelectrically conductive wall portion conformable with the surface of thexerographic plate to permit uniform close spacing of the said wallportion therewith, said manifold assembly including an exhaust conduitmeans, one end of said exhaust conduit means forming an exhaust slotextending transversely of and across the approximate center of said wallportion of said manifold assembly, a first inlet conduit means and asecond inlet conduit means in saidmanifold, one end of said first inletconduit means and one end of said second inlet conduit means extendingtransversely of said wall portion of said manifold assembly on oppositesides of said exhaust conduit means, and at opposed angles with respectto each other to form oppositely directed inlets for a powdereddeveloping material; a powdered developing source means, the other endof said first inlet conduit means and the other end of said second inletconduit means being connected to said powdered developing source means,and a vacuum means, the other end of said exhaust conduit means beingconnected to said vacuum means.

References Cited in the file of this patent UNITED STATES PATENTSHayford July-15, 1958'

